With the development of communication technologies, the 3rd Generation Partnership Project 2 (3GPP2) proposed a standard for HRPD technology in order to solve the crucial issue on air interfaces in a Code Division Multiple Access (CDMA) system. This standard aims to improve the data transmission rate on a wireless interface. Compared with the data rate of 153.6 kbit/s provided by CDMA 2000 1x, the HRPD technology may provide a forward data rate up to 2.4 Mbit/s.
In an HRPD network, a new modulation technique is utilized over air interface and methods for data rate control, scheduling optimization and time division multiplex and the like are added, which cause a significant improvement in data transmission rate over air interface. In the HRPD technology, a private data channel on a CDMA carrier (1.25 MHz) may be employed to support high rate packet data services, with a forward data rate up to 2.4576 Mbit/s, and a peak data rate of 153.6 kbit/s for a single user supported in reverse direction.
A separate carrier is needed to support HRPD when deploying an HRPD network. In this manner, when moving in the HRPD network, an access terminal may move from one AN into another AN in the HRPD network. At this time, a handoff from a source NA to a destination NA is necessary.
Currently, the 3GPP2 standard supports only the inter-AN handoff in dormant state. This handoff process is as follows: when an access terminal performing a data service in an HRPD network moves to an edge of the coverage zone of a cell, it is necessary to be handed off to another AN so as to continue its data service. At this time, the system switches the packet data service from an active state to a dormant state at the source AN, and then hands off to the destination AN in the dormant state. After moving into the destination AN, the system switches the packet data service from the dormant state back to the active state at the destination AN.
With the above handoff process, a handoff operation from a source AN to a destination AN may be implemented. However, for a data service with high real-time requirement, such as Voice over IP (VoIP), Video Phone, Push-To-Talk (PTT) and stream media, such a handoff process may cause an interruption of the service, which will result in an adverse effect to the utilization of the service for the user.
In other words, in the method of inter-AN, inter-Packet Control Function (PCF) handoff in dormant state provided in the prior art standard, it is necessary to release the Point-to-Point Protocol (PPP) connection being in use during a handoff process, and thus it is necessary for the Packet Data Service Network (PDSN) to reallocate a new PPP connection for the destination network. During the reallocation of the new PPP connection, for one thing, the service of the user may be interrupted due to the failure of the reallocation process resulted from problems of the resources; for another, the current service of the user may be delayed significantly because it will cost the PDSN some time to reestablish a PPP connection.
In view of this, a hard handoff process is required to ensure the continuity of a service during an inter-AN handoff process. However, in the prior art standard, only an inter-AN handoff process in dormant state is defined, and there is a lack of an inter-AN, inter-PCF hard handoff process in an active state in an HRPD system.